56nm pitch Cu dual-damascene interconnects with self-aligned via using negative-tone development Lithography-Etch-Lithography-Etch patterning scheme

AbstractIn the attempts to push the resolution limits of 193nm immersion lithography, this work demonstrates the building of 3 metal level 56nm pitch copper dual-damascene interconnects, using Negative-Tone Development Lithography-Etch-Lithography-Etch (LELE) Patterning at line level. Line Resistance and intra-level capacitance can be affected by the double patterning integration, but a good process window has been demonstrated, showing no impact on RC performance. The introduction of a self-aligned via (SAV) process with a TiN hard-mask is able to provide a robust process window in terms of via-metal short yield at line and via level. SAV implementation at these dimensions also affects the aspect-ratio of the structures and leads to new challenges in metallization: optimized profile, without bowing or undercut, is mandatory to enable the filling of 28nm lines. The metal hard-mask has to be removed or at least faceted by erosion. This can be achieved by conventional RIE process optimization, but pushes the RIE selectivity to challenging limits. Physical dimensions on target and via chain yield have been demonstrated by fine tuning RIE process. Profile improvement can also be achieved by the introduction of new WET process, helping the removal of the metal hard-mask while being neutral to the ULK. We have demonstrated good yield and reliability with an integration using hard-mask wet removal.